The long-term goal of this research program is to develop catheter-based optical coherence tomography (OCT) imaging tools that will improve the care of patients suffering from cardiac arrhythmias. This project aims to improve radiofrequency ablation (RFA) therapy, which is the standard of care for many arrhythmias, by providing microscopic image guidance at the tip of the catheter. This may potentially improve outcomes and safety and reduce procedure times. The specific objective of this proposal is to design, prototype, and validate a cardiac RFA catheter integrated with forward-viewing OCT imaging at the catheter tip. Cardiac arrhythmias are a major source of morbidity and mortality in the United States and catheter-based RFA through percutaneous access has emerged as the standard of care for the potential curative treatment of many arrhythmias. The goal of catheter ablation is to target and eradicate the critical component of an abnormal reentrant circuit or abnormal ectopic site by creating thermal lesions, usually on the endocardial surface of heart, while minimizing or avoiding damage to healthy, normal heart tissue. Practice of cardiac RFA requires a high level of skill and training. Electrophysiologists currently do not have real-time guidance at the cathete tip to identify critical substrates and structures to target or to avoid, to visualize catheter-tisue contact, nor to monitor the placement of a lesion or complications. Thus, current implementation of RFA in clinical practice is associated with significant unmet technological needs. Additional catheter-tip technology may decrease procedural time (and therefore radiation dose), improve outcomes and improve patient and operator safety. Previous results indicate that OCT imaging can address these unmet needs and can be accomplished within the heart via percutaneous access. Real-time, sub-surface imaging of the tissue at the catheter tip may potentially improve RFA therapy in four specific ways: (1) confirming catheter contact and orientation with the heart wall, (2) visualizing and identifying substrates to guide location of treatment sites, (3) monitorig lesion formation to confirm energy delivery, and (4) preventing complications such as steam pops, perforations, or thrombosis by detecting early signs of overtreatment, thin walls, and blood at the catheter tip. The specific aims of this design-directed project are: Aim 1: Design, prototype, and verify an integrated cardiac RFA/OCT catheter. Aim 2: Validate the primary functions of the integrated RFA/OCT catheter in animal models. The deliverable outcome of this two-year design-directed project will be an integrated RFA/OCT catheter design that is verified and validated in animal models. If successful, the results will justify further development and translation of the technology into a clinical device through large animal and clinical trials.